The Adiabatic Flow of Evaporating Fluids in Pipes of Uniform Bore

Abstract

The paper presents a theoretical investigation of the adiabatic flow of evaporating fluids in pipes, supported by experiments with water.

It is postulated, on the basis of published data, that an evaporating fluid flow will conform to one of three modes: (1) annular (2) separated, and (3) frothing.

In types (1) and (2) the liquid and vapour phases flow with different velocities.

Starting from assumptions usually made in the subject of fluid flow, theory is developed which enables the mean liquid and vapour velocities and also the associated critical outlet conditions to be calculated.

In type (3) a network of liquid maintained by surface tension operates to prevent relative motion, and standard thermodynamic theory is applicable.

In experiments with water the flow was found to be annular. By measuring the fluid momentum at the tube outlet an experimental determination of the relative velocity factor (the ratio of mean vapour velocity to mean liquid velocity) was obtained. Data given by Burnell (1947)† are also analysed.

Measured values of critical outlet pressures and relative velocity factors are in good agreement with those predicted by theory.

A chart is provided relating initial pressure, critical outlet pressure, and mass flow per unit area, over a range of initial pressures from 8 to 100 lb. per sq. in. abs. for water.